Transparent composite materials are known for use in vehicle and other applications requiring light transmission or visual transparency. Such transparent composite materials include windows or other transparent materials useful for light transmission therethrough, particularly in hostile environment and in locations requiring ballistic resistance. Such reinforcement further provides the window or transparent device resistance to cracking or breakage and/or reduced system weight.
Transparent composite materials typically include a reinforcing fiber. In order to render the composite material transparent, both the matrix material and the reinforcing fiber are fabricated from a transparent material. The materials typically do not have the same optical properties over the entire operational envelope, thus resulting in distortion. For example, the refractive index of the matrix material and the reinforcing fiber may not be the same, resulting in a bending or refracting of the light passing through the composite.
Geometry of reinforcing fibers also affects the distortion of light passing through the transparent device. For example, round fibers (i.e., fibers having circular cross-sections) provide prismatic or other optical light refractive effects that provide overall distortion of the light passing through the transparent device.
In addition, the optical properties of the matrix material and reinforcing fiber may be dependent upon temperature, wherein the materials in the matrix and the materials in the reinforcing material have optical properties that are independently dependent upon temperature. Known reinforcing systems suffer from the drawback that applications with a high temperature variation, including operation in locations having high ambient temperatures results in a large change in optical properties (e.g., change in refractive index), which provides increased distortion of light passing through the transparent device.
What is needed is a transparent reinforcing material is that is resistant to light distortion at various temperatures and does not suffer from the drawbacks of the prior art.